Capacitors have widely been used in various electronic components, backup or recovery power sources, and power storages for hybrid automobiles or fuel cell vehicles.
FIG. 28 is a cross sectional view of a conventional capacitor 5001. A capacitor element 10 includes collectors made of aluminum foil and a pair of positive and negative electrodes having polarized layers on the collectors, respectively. The pair of electrodes deviate from each other in opposite directions and rolled with a separator provided between the electrodes, thus providing the capacitor element 10. A positive electrode and a negative electrode are connected with end surfaces 10B and 10C of the capacitor element 10, respectively. The capacitor 10 has a hollow 10A provided in the center thereof.
The capacitor element 10 is accommodated together with an electrolyte in a cylindrical metal case 11 which is made of aluminum and which has a bottom 11C. A projection 11A is provided unitarily with the bottom 11C of the metal case 11 so that the projection 11A is engaged into the hollow 10A of the capacitor element 10. The end surface 10C of the negative electrode of the capacitor element 10 is joined mechanically and electrically to the bottom 11C of the metal case 11 by a joining method, such as laser welding. The metal case 11 has a narrowed portion 11B having a cross-section having a V-shape, and thus, has a locally small diameter at the narrowed portion 11B. The narrowed portion 11B holds a rim of the end surface 10B of the capacitor element 10 from outside.
A positive terminal 12A for external connection is formed unitarily with an outer surface of a terminal plate 12. An inner surface of terminal plate 12 has a joining region 12B having the end surface 10B of the capacitor element 10 joined thereto. A projection 12C of the terminal plate 12 is engaged into the hollow 10A of the capacitor element 10. The end surface 10B of the capacitor element 10 is joined mechanically and electrically to the joining region 12B of the terminal plate 12 by a joining method, such as laser welding.
An insulating ring 13 having a ring shape is provided on an upper part of the narrowed portion 11B of the metal case 11. The insulating ring 13 extends from between an inner surface of the metal case 11 and an outer side surface of the terminal plate 12 to a portion of a rim of an inner surface of the terminal plate 12 for electrically insulating the terminal plate 12 from the metal case 11.
A sealing rubber 14 having a ring shape made of insulating rubber is provided on a rim of an outer surface of the terminal plate 12. An upper end of the metal case 11 is curled together with the sealing rubber 14 at the opening 11D (by a curling process) so as to allow the terminal plate 12 to seal the metal case 11.
The metal case 11 of the conventional capacitor 5001 is sealed mechanically. The capacitor element 10 generates heat during its use under hostile atmosphere or conditions or during a life durability test. This heat raises the temperature of the electrolyte and the pressure in the metal case 11, and may consequently cause the electrolyte to leak from the metal case 11.
FIG. 29 is a cross-sectional view of another conventional capacitor 5002 disclosed in Japanese Patent Laid-pen Publication No. 2000-315632. A capacitor element 111 includes collectors made of aluminum foil and a pair of positive and negative electrodes having polarized layers provided on the collectors, respectively. The pair of electrodes deviate from each other in opposite directions and rolled together with a separator between the electrodes, thus providing the capacitor element 111. A positive electrode and a negative electrode are connected with portions 111A and 111B of the collectors exposing at end surfaces 111C and 111D of the capacitor element 111, respectively.
The capacitor element 111 is accommodated together with an electrolyte in a cylindrical metal case 112 which is made of aluminum and has a bottom 112B thereof. A projection 112A is provided unitarily with the bottom 112B of the metal case 112 for positioning and fixing the capacitor element 111. A sealing plate 113 is joined to the end surface 111C of the capacitor element 111 so as to seal an opening 112C of the metal case 112. A projection 113A is provided on the sealing plate 113 for positioning and fixing the capacitor element 111. The capacitor 5002 further includes an insulator 114, terminals 115 for external connection, and a core 116 which has a bar shape and is provided at the center of the capacitor element 111. The sealing plate 113 has a communication aperture 117 provided therein for supplying the electrolyte.
In the conventional capacitor 5002, the metal case 112 and the sealing plate 113 function as collectors.
FIG. 30 illustrates plural capacitors 5002 connected to each other. The terminals 115 of the capacitor 5002 deviate in directions 5002B and 5002C opposite to each other with respect to a center axis 5002A of the metal case 112. This arrangement of the capacitors 5002 allows the terminals 115 joined onto each other at the center axis 5002A of the metal case 112. Even if the capacitors 5002 are mounted onto an upper surface of a board 118, any one of the capacitors 5002 does not apart from the board 118, and thus, the capacitors 5002 are connected to each other accurately, hence providing a capacitor unit.
In the conventional capacitor 5002, if the sealing plate 113 is connected to the positive electrode of the capacitor element 111, the sealing plate 113 and the metal case 112 becomes a positive terminal and a negative terminal, respectively.
The sealing plate 113 of the positive terminal and the metal case 112 of the negative terminal are electrically insulated from each other with the insulator 114. The distance between the sealing plate 113 and the metal case 112 is extremely small, accordingly causing the short-circuit between the positive and negative terminals due to water drops condensed depending on the environment of usage. Then, electric charges stored in the metal case 112 is consumed at the position where the short-circuit occurs, thereby preventing the capacitor from functioning.
FIG. 31 is a cross sectional view of a further conventional capacitor 5003 disclosed in Japanese Patent Laid-Open Publication No. 2000-315632. A capacitor element 220 includes collectors made of aluminum foil and a pair of positive and negative electrodes having polarized layers provided on the collectors, respectively. The electrodes deviate from each other in opposite directions and rolled with a separator provided between the electrodes, thus providing the capacitor element 220. A positive electrode and a negative electrode are connected with end surfaces 220A and 220B of the capacitor element 220, respectively.
The capacitor element 220 is accommodated together with an electrolyte in a cylindrical metal case 221 made of aluminum. The metal case has a bottom 221B. A projection 221A having a cross section having a polygonal shape is formed unitarily with the bottom 221B of the metal case 221 for positioning and fixing the capacitor element 220. The end surface 220B of the capacitor element 220 is joined to the bottom 221B of the metal case 221.
A sealing plate 222 made of aluminum is joined to the end surface 220A of the capacitor element 220. The sealing plate 222 has a projection 222A having a cross section of the polygonal shape provided on an inner surface of the sealing plate for positioning and fixing the capacitor element 220. A portion 223 of the sealing plate 222 is subjected to an alumite process. The capacitor 5003 further includes a terminal 224 having a planer shape and having an aperture provided therein for external connection, a terminal 225 having a planer shape and having an aperture provided therein for external connection, a core 226 having a bar shape provided at the center of the capacitor element 220, and a pressure control valve 227. The core 226 has a hollow therein. The sealing plate 222 has a communication aperture 222B provided therein for feeding the electrolyte.
The capacitor element 220 of the conventional capacitor 5003 has one electrode connected to the terminal 224 joined to sealing plate 222, and has another electrode connected to the terminal 225 joined to the metal case 221.
FIG. 32 illustrates plural capacitors 5003 connected to each other. The terminals 224 and 225 of the planer shapes of the capacitor 5002 deviate in directions 5003B and 5003C opposite to each other with respect to a center axis 5003A of the metal case 221. This arrangement of the capacitors 5003 allows the terminals 224 and 225 joined onto each other at the center axis 5003A of the metal case 221. Even if the capacitors 5003 are mounted onto an upper surface of a board 228, any one of the capacitors 5003 does not apart from the board 228, and thus, the capacitors 5003 are connected to each other accurately, hence providing a capacitor unit.
In the conventional capacitor 5003, if the negative electrode of the capacitor element 220 is connected to the sealing plate 222, the sealing plate 222 becomes the negative terminal. When the capacitor 5003 is used under a high temperature and a high humidity with the sealing plate 222 being the negative terminal, the electrolyte may enter into the interface between the sealing plate 222 and a rubber material of the pressure control valve 227, thus hence leaking to outside.
Since the sealing plate 223 is the negative terminal, aluminum composing the sealing plate 222 causes the following electro-chemical reaction with water in the electrolyte near the rubber material of the pressure control valve 227, thus producing hydroxide ion.H2O+1/2O2+4e−→2OH−The hydroxide ion and positive ion in the electrolyte causes the electrolyte to exhibit a strong alkaline property. The electrolyte exhibiting the alkaline property may enter into the interface between the sealing plate 222 and the rubber material and contact the whole surface of the rubber material of the pressure control valve 227. The entering electrolyte may cut a chemical bridge structure of the rubber material and have the quality of the rubber material deteriorate, accordingly preventing the rubber material from having a sealing effect and allowing the electrolyte to leak out.
If a slight gap is provided at the interface between the sealing plate 222 and the rubber material, the electrolyte exhibiting the alkaline property alkali may enter the gap due to the surface tension of the electrolyte and then, may leak. In order to prevent the leaking, the sealing plate 222 is attached securely to the rubber material.
In the case that the positive electrode of the capacitor element 220 is joined to the sealing plate 222 to thus be the positive terminal and that the electrolyte contains tetra-ethyl-ammonium-fluoroborate as solute of the electrolyte, the negative ion in the electrolyte, that is, tetra-fluoroborate anion causes the following electro-chemical reaction near the sealed opening of the metal case 221.BF4−+H2O⇄BF3(OH)−+HF,HF+H2O→H3O++F−The above reaction produces hydronium ion in the electrolyte, accordingly causing the electrolyte to exhibit a strong acidic property near the sealing plate 222. The electrolyte exhibiting the acidic property may enter into the interface between the sealing plate 222 and the rubber material of the pressure control valve 227 and contact the sealing plate 222 and the whole surface of the rubber material, thereby causing the surface of the sealing plate 222 and the rubber material to deteriorate and causing its sealing effect to decline.
FIG. 33 is a cross sectional view of a still further conventional capacitor 5004 disclosed in Japanese Patent Laid-Open Publication No. 2000-315632. A capacitor element 310 includes collectors made of aluminum foil and a pair of positive and negative electrodes having polarized layers provided on the collectors, respectively. The electrodes deviate from each other in opposite directions and rolled with a separator provided between the electrodes, thus providing the capacitor element 310. A positive electrode and a negative electrode are connected with end surfaces 310A and 310B of the capacitor element 310, respectively.
A metal plate 311 is joined to the end surface 310A of the capacitor element 310. The capacitor element 310 is accommodated together with an electrolyte in a cylindrical metal case 312 which is made of aluminum and has a bottom 312D thereof. A projection 312A is provided on the bottom 312D of the metal case 312. The metal case 312 has a diameter reduced annularly near an opening 312E, thereby providing a narrowed portion 312B. A sealing plate 313 made of insulating material seals the opening 312B of the metal case 312. A core 314 having a bar shape has a terminal 314A at an end thereof for external connection. A terminal 315 for external connection is joined to an outer surface of the metal case 312. The core 314 and the metal case 312 are electrically insulated from each other with an insulator 316. A plug 317 made of elastic, insulating material, such as rubber, is provided in combination with a cap 318 to form a pressure control valve. The capacitor 5004 further includes an O-ring 319 and a sealing rubber 320. The sealing rubber 320 is provided on a periphery of an upper surface of the sealing plate 313. The metal case 312 has a portion 312C curled at the opening 312E thereof. The sealing rubber 320 is compressed with the curled portion 312C, thereby sealing between the metal case 312 and the sealing plate 313.
The electrode, the end surface 310B, of the capacitor element 310 is electrically connected to the bottom 312D of the metal case 312. The end surface 310A of the capacitor element 310 is joined to the metal plate 311. A core 314 having a bar shape is provided at the center of the capacitor element 310 and joined to the metal plate 311. The sealing plate 313 has a through-hole 313A through which the terminal 314A extends. The opening 312E of the metal case 312 is sealed with the sealing plate 313. The metal case 313 functions as a collector terminal.
FIG. 34 illustrates plural capacitors 5004 connected to each other. The terminals 31A and 315 of the capacitors 5002 having planer shapes deviate in directions 5004B and 5004C opposite to each other with respect to a center axis 5004A of the metal case 312. This arrangement of the capacitors 5004 allows the terminals 31A and 315 joined onto each other at the center axis 5004A of the metal case 312. Even if the capacitors 5004 are mounted onto an upper surface of a board 321, any one of the capacitors 5004 does not apart from the board 321, and thus, the capacitors 5004 are connected to each other accurately.
The conventional capacitor 5004 however can hardly have a small size, a large capacitance, a small resistance, or a low cost. The metal plate 311 and the core 314 connected with the electrode at the end surface 310A of the capacitor element 310 extend across the sealing plate 313, thus providing a large electrical resistance and being prevented from having a small size and a low cost.